Multi-objective optimization for active power management of synchronous motor drives

Abstract

A method of controlling operation of an electric machine includes: determining a voltage-based torque limit based on a voltage constraint of a direct current (DC) bus supplying power to an inverter for powering the electric machine; determining a motor current-based torque limit based on a motor current limit; determining a supply current-based torque limit based on a supply rating, to supply current to the inverter, of the DC bus; determining a regenerative current-based torque limit based on a receive rating, to receive current from the inverter, of the DC bus; determining a final torque limit based on the voltage-based torque limit, the motor current-based torque limit, the supply current-based torque limit, and the regenerative current-based torque limit; determining a limited command torque based on a torque command and the final torque limit; and calculating at least one current command based on, at least, the limited command torque.

What is claimed is: 
     
       1. A method of controlling operation of an electric machine, comprising:
 determining a voltage-based torque limit based on a voltage constraint of a direct current (DC) bus supplying power to an inverter for powering the electric machine; 
 determining a motor current-based torque limit based on a motor current limit; 
 determining a supply current-based torque limit based on a supply rating, to supply current to the inverter, of the DC bus; 
 determining a regenerative current-based torque limit based on a receive rating, to receive current from the inverter, of the DC bus; 
 determining a final torque limit based on the voltage-based torque limit, the motor current-based torque limit, the supply current-based torque limit, and the regenerative current-based torque limit; 
 determining a limited command torque based on a torque command and the final torque limit; and 
 calculating at least one current command based on, at least, the limited command torque. 
 
     
     
       2. The method of  claim 1 , further comprising selectively controlling a plurality of switches within the inverter to cause the inverter to supply a current to the electric machine based on the at least one current command. 
     
     
       3. The method of  claim 1 , wherein the motor current limit is a lesser one of a current limit of the electric machine and a current limit of the inverter. 
     
     
       4. The method of  claim 1 , wherein determining the final torque limit further comprises arbitrating between the voltage-based torque limit and the motor current-based torque limit. 
     
     
       5. The method of  claim 4 , wherein arbitrating between the voltage-based torque limit and the motor current-based torque limit further comprises:
 determining a first motor current-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the motor current limit; 
 determining a second motor current-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the motor current limit; 
 determining a first voltage limit-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the voltage constraint of the DC bus; 
 determining a second voltage limit-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the voltage constraint of the DC bus; 
 determining one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having a lesser value; 
 determining one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having a lesser value; and 
 selecting one of the motor current-based torque limit and the voltage-based torque limit based on the one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having the lesser value and based on the one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having the lesser value. 
 
     
     
       6. The method of  claim 5 , wherein selecting the one of the motor current-based torque limit and the voltage-based torque limit further comprises:
 selecting the motor current-based torque limit as the final torque limit in response to determining the first motor current-based q-axis current being less than the first voltage limit-based q-axis current, and the second motor current-based q-axis current being less than the second voltage limit-based q-axis current; and 
 selecting the voltage-based torque limit as the final torque limit in response to determining the first voltage limit-based q-axis current being less than the first motor current-based q-axis current, and the second voltage limit-based q-axis current being less than the second motor current-based q-axis current. 
 
     
     
       7. The method of  claim 4 , wherein arbitrating between the voltage-based torque limit and the motor current-based torque limit further comprises:
 determining a first motor current-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the motor current limit; 
 determining a second motor current-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the motor current limit; 
 determining a first voltage limit-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the voltage constraint of the DC bus; 
 determining a second voltage limit-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the voltage constraint of the DC bus; 
 determining one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having a lesser value; 
 determining one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having a lesser value; 
 determining the one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having the lesser value corresponding to a different constraint from the one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having the lesser value; 
 determining a d-axis intersection current value where a q-axis current corresponding to the motor current limit is equal to a q-axis current corresponding to the voltage constraint of the DC bus; and 
 determining the final torque limit based on the d-axis intersection current value and based on the q-axis current corresponding to each of motor current limit and the voltage constraint of the DC bus. 
 
     
     
       8. The method of  claim 1 , wherein determining the regenerative current-based torque limit includes determining a regenerative current and motor current-based torque limit based on an intersection of d-axis and q-axis currents to satisfy each of the receive rating and the motor current limit. 
     
     
       9. The method of  claim 8 , further comprising:
 calculating a voltage generated by the inverter based on the regenerative current and motor current-based current limit; and 
 determining if the voltage generated by the inverter based on the regenerative current and motor current-based current limit satisfies the voltage constraint of the DC bus to verify the intersection of d-axis and q-axis currents to satisfy each of the receive rating and the motor current limit. 
 
     
     
       10. The method of  claim 1 , further comprising:
 calculating a first y-intercept of a plot of d-axis current versus q-axis current, with the d-axis current and the q-axis current each corresponding to the inverter satisfying the receive rating; 
 calculating a second y-intercept of the plot of d-axis current versus q-axis current, with the d-axis current and the q-axis current each corresponding to the inverter satisfying the receive rating; and 
 determining if the electric machine can be operated in an a regenerative mode while satisfying the motor current limit, including, based on a velocity of the electric machine, one of:
 determining if the motor current limit is greater than the first y-intercept of the plot of d-axis current versus q-axis current, and the first y-intercept of the plot of d-axis current versus q-axis current is greater than a negation of the motor current limit, and the negation of the motor current limit is greater than the second y-intercept of the plot of d-axis current versus q-axis current; and 
 determining if: the motor current limit is less than the first y-intercept of the plot of d-axis current versus q-axis current, and the motor current limit is greater than the second y-intercept of the plot of d-axis current versus q-axis current, and the negation of the motor current limit is less than the second y-intercept of the plot of d-axis current versus q-axis current. 
 
 
     
     
       11. A control system for controlling operation of an electric machine, comprising:
 a processor; and 
 a memory that includes instructions that, when executed by the processor, cause the processor to:
 determine a voltage-based torque limit based on a voltage constraint of a direct current (DC) bus supplying power to an inverter for powering the electric machine; 
 determine a motor current-based torque limit based on a motor current limit; 
 determine a supply current-based torque limit based on a supply rating, to supply current to the inverter, of the DC bus; 
 determine a regenerative current-based torque limit based on a receive rating, to receive current from the inverter, of the DC bus; 
 determine a final torque limit based on the voltage-based torque limit, the motor current-based torque limit, the supply current-based torque limit, and the regenerative current-based torque limit; 
 determine a limited command torque based on a torque command and the final torque limit; and 
 calculate at least one current command based on, at least, the limited command torque. 
 
 
     
     
       12. The control system of  claim 11 , wherein the instructions further cause the processor to selectively control a plurality of switches within the inverter to cause the inverter to supply a current to the electric machine based on the at least one current command. 
     
     
       13. The control system of  claim 11 , wherein the motor current limit is a lesser one of a current limit of the electric machine and a current limit of the inverter. 
     
     
       14. The control system of  claim 11 , wherein determining the final torque limit further comprises arbitrating between the voltage-based torque limit and the motor current-based torque limit. 
     
     
       15. The control system of  claim 14 , wherein arbitrating between the voltage-based torque limit and the motor current-based torque limit further comprises the instructions causing the processor to:
 determine a first motor current-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the motor current limit; 
 determine a second motor current-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the motor current limit; 
 determine a first voltage limit-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the voltage constraint of the DC bus; 
 determine a second voltage limit-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the voltage constraint of the DC bus; 
 determine one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having a lesser value; 
 determine one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having a lesser value; and 
 select one of the motor current-based torque limit and the voltage-based torque limit based on the one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having the lesser value and based on the one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having the lesser value. 
 
     
     
       16. The control system of  claim 15 , wherein selecting the one of the motor current-based torque limit and the voltage-based torque limit further comprises the instructions causing the processor to:
 select the motor current-based torque limit as the final torque limit in response to determining the first motor current-based q-axis current being less than the first voltage limit-based q-axis current, and the second motor current-based q-axis current being less than the second voltage limit-based q-axis current; and 
 select the voltage-based torque limit as the final torque limit in response to determining the first voltage limit-based q-axis current being less than the first motor current-based q-axis current, and the second voltage limit-based q-axis current being less than the second motor current-based q-axis current. 
 
     
     
       17. The control system of  claim 14 , wherein arbitrating between the voltage-based torque limit and the motor current-based torque limit further comprises the instructions causing the processor to:
 determine a first motor current-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the motor current limit; 
 determine a second motor current-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the motor current limit; 
 determine a first voltage limit-based q-axis current corresponding to a d-axis current having a predetermined minimum value and corresponding to the voltage constraint of the DC bus; 
 determine a second voltage limit-based q-axis current corresponding to the d-axis current having a predetermined maximum value and corresponding to the voltage constraint of the DC bus; 
 determine one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having a lesser value; 
 determine one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having a lesser value; 
 determine the one of the second motor current-based q-axis current and the second voltage limit-based q-axis current having the lesser value corresponding to a different constraint from the one of the first motor current-based q-axis current and the first voltage limit-based q-axis current having the lesser value; 
 determine a d-axis intersection current value where a q-axis current corresponding to the motor current limit is equal to a q-axis current corresponding to the voltage constraint of the DC bus; and 
 determine the final torque limit based on the d-axis intersection current value and based on the q-axis current corresponding to each of motor current limit and the voltage constraint of the DC bus. 
 
     
     
       18. The control system of  claim 11 , wherein determining the regenerative current-based torque limit further comprises the instructions causing the processor to determine a regenerative current and motor current-based torque limit based on an intersection of d-axis and q-axis currents to satisfy each of the receive rating and the motor current limit. 
     
     
       19. The control system of  claim 18 , further comprising the instructions causing the processor to:
 calculate a voltage generated by the inverter based on the regenerative current and motor current-based current limit; and 
 determine if the voltage generated by the inverter based on the regenerative current and motor current-based current limit satisfies the voltage constraint of the DC bus to verify the intersection of d-axis and q-axis currents to satisfy each of the receive rating and the motor current limit. 
 
     
     
       20. The control system of  claim 11 , further comprising the instructions causing the processor to:
 calculate a first y-intercept of a plot of d-axis current versus q-axis current, with the d-axis current and the q-axis current each corresponding to the inverter satisfying the receive rating; 
 calculate a second y-intercept of the plot of d-axis current versus q-axis current, with the d-axis current and the q-axis current each corresponding to the inverter satisfying the receive rating; and 
 determine if the electric machine can be operated in an a regenerative mode while satisfying the motor current limit, including, based on a velocity of the electric machine, one of:
 determine if the motor current limit is greater than the first y-intercept of the plot of d-axis current versus q-axis current, and the first y-intercept of the plot of d-axis current versus q-axis current is greater than a negation of the motor current limit, and the negation of the motor current limit is greater than the second y-intercept of the plot of d-axis current versus q-axis current; and 
 determine if: the motor current limit is less than the first y-intercept of the plot of d-axis current versus q-axis current, and the motor current limit is greater than the second y-intercept of the plot of d-axis current versus q-axis current, and the negation of the motor current limit is less than the second y-intercept of the plot of d-axis current versus q-axis current.